Heretofore, polyamide films containing a nylon resin have been widely used in various fields as films having desirable gas barrier properties, toughness, pinhole resistance, and the like.
In order to impart dimensional stability and aroma retention to such polyamide films, multilayer films with polyester/polyamide/polyester laminated thereon have been disclosed (for example, Patent Literatures 1 and 2).
The multilayer films disclosed in Patent Literatures 1 and 2 exhibit the aforementioned excellent properties. However, a problem occurs, for example, if the multilayer films disclosed in Patent Literatures 1 and 2 are formed into a packaging film by laminating a sealing layer formed of an olefin-based resin or the like thereon by dry lamination etc. The problem is that when the lamination strength between the multilayer film and the sealing layer is measured, delamination occurs between the polyester/polyamide layers on the side on which the sealing layer is laminated. Therefore, its lamination strength is sometimes immeasurable. If the lamination strength is immeasurable, the quality of the packaging film cannot be checked. Therefore, a film with polyamide and polyester laminated therein having excellent lamination characteristics has been desired.
A multilayer stretched polyamide-based film composed of a multilayer stretched film comprising a polyamide resin layer (X)/polyamide resin layer (Y), wherein the polyamide resin layer (Y) contains amorphous polyamide, has been disclosed (for example, Patent Literature 3).
Patent Literature 3 discloses that the multilayer film of Patent Literature 3 is excellent in heat resistance, transparency, gas barrier properties and pinhole resistance. However, when the multilayer film is used as a packaging film for wrapping foods and the like, leakage of the aroma of the content and the like are observed. This results in deterioration of the quality or commercial value of the content, and is thus undesirable. Therefore, packaging films are required to have high aroma retention. Furthermore, when the multilayer film is used as a packaging film that is subjected to more severe boiling treatment or retort treatment, higher thermal dimensional stability is required.
Multilayer stretched polyamide-based films are distributed as packaging films for wrapping foods and the like, and pinholes may occur due to abrasion while they are being conveyed, transported, etc. Such pinholes impair the excellent gas barrier properties of the multilayer film. Accordingly, multilayer films having excellent bending resistance have been desired in the market.